Last Updated November 14th, 2016: Updated to include that this works under FreeBSD 11.0 as well. Really anything between FreeBSD 9 and 11 should work.

April 30th, 2015: This article is really popular, I’ll do my best to keep it up to date! I’ve added notes about TRIM, alignment and GMIRROR (-h) labeling since it was originally posted.

Note: These instructions have been verified to work for FreeBSD 9.1, FreeBSD 9.2, FreeBSD 10.0, FreeBSD 10.1, and FreeBSD 11.0 .

By default gmirror and the GPT partitioning scheme do not get along.  This is because both GEOM (the provider for gmirror) and GPT write meta data at the end of the disk.

Note: Instructions on rebuiling a gmirror with this kind of setup are at the bottom under Testing & Replacing A Failed Disk.

The concept behind this procedure and “work around” is that instead of mirroring the entire disk, you use gmirror to mirror each of your partitions.

The order of these steps is important to avoid corruption.  I would only do this on a clean install (and these directions are for that).  If you setup a gmirror after the fact on a running machine the gmirror meta data has to get written somewhere, and if you’ve got a file system on it with data, you risk corrupting it and losing data if it happens to be at the end.

To avoid this we’ll setup GPT, create the partitions, create the gmirror providers and finally newfs the appropriate partition.  This ensures nothing will get corrupted.

Step 1: Boot The FreeBSD Installer

Start the FreeBSD install process as normal.  When you are asked about how you want to partition the disk pick “Shell”:

FreeBSD 9 installer

Step 2: Setup The Partitions

Once inside the shell here are the commands to setup GPT and slice up both disks.  These examples assume you are doing this on disk ‘ada0’ and ‘ada1’ (SATA), if you are using SCSI you’d do da0, da1. We also align the partitions to 1 MiB boundaries which will work with 4k (or advanced format) disks, for more information on this read my post about partition alignment under FreeBSD for 4k disks.

# ---- Setup 1st disk
gpart create -s gpt ada0
gpart add -s 128k -t freebsd-boot -l boot0 ada0
gpart add -a 1m -s 8G -t freebsd-swap -l swap0 ada0
gpart add -a 1m -t freebsd-ufs -l root0 ada0

# -- Install boot code to first disk
gpart bootcode -b /boot/pmbr -p /boot/gptboot -i 1 ada0

# ---- Setup 2nd disk
gpart create -s gpt ada1
gpart add -s 128k -t freebsd-boot -l boot1 ada1
gpart add -a 1m -s 8G -t freebsd-swap -l swap1 ada1
gpart add -a 1m -t freebsd-ufs -l root1 ada1

# -- Install boot code to 2nd disk
gpart bootcode -b /boot/pmbr -p /boot/gptboot -i 1 ada1

Step 3: Setup The Gmirror Providers

Before we proceed we need to have GEOM “re-taste” the partitions so our nice labels show up in /dev/gpt/:

true > /dev/ada0
true > /dev/ada1

You can check to make sure this worked by running:

ls -l /dev/gpt/

# Output should look similar to this:
crw-r-----  1 root  operator    0, 100 /dev/gpt/boot0
crw-r-----  1 root  operator    0, 108 /dev/gpt/boot1
crw-r-----  1 root  operator    0, 102 /dev/gpt/root0
crw-r-----  1 root  operator    0, 110 /dev/gpt/root1
crw-r-----  1 root  operator    0, 104 /dev/gpt/swap0
crw-r-----  1 root  operator    0, 112 /dev/gpt/swap1

Now we can continue to build the mirror providers for each of our partitions:

# -- Build gmirrors
gmirror label -h boot /dev/gpt/boot0 /dev/gpt/boot1
gmirror label -h swap /dev/gpt/swap0 /dev/gpt/swap1
gmirror label -h root /dev/gpt/root0 /dev/gpt/root1
# -- Load the geo_mirror KLD
kldload geom_mirror

# -- Check status
gmirror status

# -- You should see something like this:
       Name    Status  Components
mirror/root  COMPLETE  gpt/root1 (ACTIVE)
                       gpt/root0 (ACTIVE)
mirror/swap  COMPLETE  gpt/swap1 (ACTIVE)
                       gpt/swap0 (ACTIVE)
mirror/boot  COMPLETE  gpt/boot1 (ACTIVE)
                       gpt/boot0 (ACTIVE)

NOTE: If you wish to have proper kernel dumps you’ll need to add -b prefer to the gmirror label operation for swap, for example:

gmirror label -b prefer -h swap /dev/gpt/swap0 /dev/gpt/swap1

This will reduce performance to the equivalent of a single physical disk as I/O operations will no longer use both simultaneously.

Step 4: Create And Mount The Root (/) Filesystem

Here we actually format the root filesystem, enabling soft updates (-U).  I also use “-L root” to set the filesystem label but this isn’t needed.  Then we mount the new filesystem in /mnt (which is where the installer expects the target filesystem to be).

If you are using SSDs add the -t option to the newfs call below so that TRIM support is enabled from the start.

# -- For HDDs:
newfs -U -L root /dev/mirror/root
# -- For SSDs:
newfs -t -U -L root /dev/mirror/root

mount /dev/mirror/root /mnt

We now need to create the fstab file which will be put into place by the installer:

vi /tmp/bsdinstall_etc/fstab
# Device          Mountpoint      FStype  Options Dump    Pass#
/dev/mirror/swap  none            swap    sw      0       0
/dev/mirror/root  /               ufs     rw      1       1

Exit out of the partitioning shell to resume the setup:


Step 5: Resume The Setup

Continue through the rest of the install as you normally would do.  At the very end when you exit the installer you will see the prompt below:

FreeBSD 9 installer

Pick Yes.

Step 6: Final Configuration

Inside this shell we just need to set a few last minute things to make sure our new OS loads GEOM on boot and also reports the mirror status in the daily report emails.

# -- Make sure gmirror module comes up on boot
echo 'geom_mirror_load="YES"' >> /boot/loader.conf

# -- Enable daily status reporting
echo 'daily_status_gmirror_enable="YES"' >> /etc/periodic.conf

And that’s it! Exit out of this shell:


And reboot!

Addendum: Testing & Replacing A Failed Disk

To test your gmirror you can pull a disk out of a gmirror and the server should log a message in dmesg(8) but otherwise function normally.  When you re-insert the disk it will rebuild automatically as gmirror will recognize it (be sure to let it rebuild fully before yanking another disk).

If you have a failed disk that needs replacing simply remove it and insert the new disk of the same size or greater (gmirror will only use the original size though).  If your hardware supports hot-swap this can be done while the server is running.  With the new disk in place we’ll need to re-partition in like we originally did above, tell gmirror to forget the old disk’s partitions and add the new disk’s partitions to the mirror containers.

Let’s assume for this example that ada1 has failed.  Once the new disk has been inserted you’ll first want to make sure it’s blank by running:

gpart show ada1

If anything but a blank listing comes up (and your replacement disk is new) think long and hard! Make sure you’ve got the correct disk and device name!

If you are using a recycled disk that isn’t blank, first blank out it’s partition (again, double check the device name!):

gpart destroy -F ada1

Now we’ll partition the disk the way the originals are (above), adjust for any differences in your own partitioning:

gpart create -s gpt ada1
gpart add -a 1m -s 128k -t freebsd-boot -l boot1 ada1
gpart add -s 8G -t freebsd-swap -l swap1 ada1
gpart add -t freebsd-ufs -l root1 ada1
gpart bootcode -b /boot/pmbr -p /boot/gptboot -i 1 ada1

Have FreeBSD re-taste the /dev/gpt/ device names:

true > /dev/ada1
ls -l /dev/gpt/

This is not needed for FreeBSD 10 and later

Now for each parition tell gmirror to forget any disk’s partitions which aren’t currently present and add the new partitions to become mirrored (remember we’re gmirroring each parittion individually instead of each disk so GPT can work happily with gmirror):

gmirror forget boot
gmirror insert -h boot /dev/gpt/boot1

gmirror forget swap
gmirror insert -h swap /dev/gpt/swap1

gmirror forget root 
gmirror insert -h root /dev/gpt/root1

Finally check the status of the rebuild:

gmirror status

More information can be found at the FreeBSD Handbook’s page on RAID1 mirroring.

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27 Responses to “HOW TO: Installing FreeBSD with gmirror (software RAID 1) and the GPT partitioning scheme”

  1. rizza

    i try to mirroring with freebsd 10 but i found a problem while insert mirror root.
    gmirror insert root /dev/gpt/root1
    problem = gmirror: provider gpt/root1 too small.
    in my case root ada0 and ada1 had same size.
    please help me ass soon as possible

    thank you

    • Adam Strohl

      Hey Rizza, it sounds like when you created the partition it got made too small as the error implies, can you show me the output of ‘gpart show’ ?

  2. Lost

    This does not work on FreeBSD 10.

    Please provide actual instructions to “Resume the setup”. You completely miss the actual partitioning in the installer, it’s not even mentioned. So how do I handle disks inside the installer?


    • Adam Strohl

      I haven’t had a chance to update the instructions yet, the title of the article doesn’t claim it to work for 10.

      Regarding missing “partitioning in the installer” the whole point is you cannot use the installer to do it and need to manually partition, thus all the instructions above thew “resume the setup” portion where you manually partition the drive.

      The installer’s partitioning system cannot do these tasks which is why I wrote the instructions in the first place.

    • Krissada Jindanupajit

      It work perfectly on FreeBSD 10 (GENERIC)…

      After you mount all new file systems to /mnt, just type “exit” and it will resume the setup.

      root@pbx:~ # gmirror status
      Name Status Components
      mirror/boot COMPLETE ada0p1 (ACTIVE)
      ada1p1 (ACTIVE)
      mirror/swap COMPLETE ada0p2 (ACTIVE)
      ada1p2 (ACTIVE)
      mirror/root COMPLETE ada0p3 (ACTIVE)
      ada1p3 (ACTIVE)
      mirror/var COMPLETE ada0p4 (ACTIVE)
      ada1p4 (ACTIVE)
      mirror/tmp COMPLETE ada0p5 (ACTIVE)
      ada1p5 (ACTIVE)
      mirror/usr COMPLETE ada0p6 (ACTIVE)
      ada1p6 (ACTIVE)
      root@pbx:~ # uname -a
      FreeBSD pbx 10.0-RELEASE FreeBSD 10.0-RELEASE #0 r260789: Fri Jan 17 01:46:25 UTC 2014 i386
      root@pbx:~ #

  3. Krissada Jindanupajit

    For the partitioning, if you want /usr /var and /tmp in different partition from / just
    setup your additional partitions ….

    # Follow Adam's instruction but when you create partition, just do what you want
    # (Replace X with 0 for ada0 and then 1 for ada1)
    gpart create -s gpt adaX
    gpart add -s 64k -t freebsd-boot -l bootX adaX
    gpart add -s 8G -t freebsd-swap -l swapX adaX
    gpart add -s 2G -t freebsd-ufs -l rootX adaX
    gpart add -s 2G -t freebsd-ufs -l varX adaX
    gpart add -s 1G -t freebsd-ufs -l tmpX adaX

    # without -s, gpart will use the remaining of your disk
    gpart add -t freebsd-ufs -l usrX adaX


    And when you build the mirrors, just do it for other partition.

    gmirror label root /dev/gpt/root0 /dev/gpt/root1
    gmirror label var /dev/gpt/var0 /dev/gpt/var1
    gmirror label tmp /dev/gpt/var0 /dev/gpt/tmp1
    gmirror label usr/dev/gpt/var0 /dev/gpt/usr1

    Do newfs then mount everything to /mnt

    newfs -U -L root /dev/mirror/root
    newfs -U -L var /dev/mirror/var
    newfs -U -L tmp /dev/mirror/tmp
    newfs -U -L usr /dev/mirror/usr

    mount /dev/mirror/root /mnt
    mkdir /mnt/var
    mount /dev/mirror/var /mnt/var
    mkdir /mnt/tmp
    mount /dev/mirror/tmp /mnt/tmp
    mkdir /mnt/usr
    mount /dev/mirror/usr /mnt/usr

    And just type “exit”, it will resume setup operation, then just follow Adam’s instruction.

    Thanks Adam for this post…

      • Adam Strohl

        I merged your correction into your original comment so that should be correct now 🙂

        • rizza

          i just follow intruction from Krissada to partition var,tmp,usr and now i found new problem.
          when i reboot without dvd ,its written

          gptboot: no /boot/loader on 0:ad(0p3)
          gptboot: no /boot/kernel/kernel on 0:ad(0p3)

          can you solve my case as fast as you can?
          please help me to solve my problem sir.

  4. koorosh

    can you create guide for raid 10 too !?
    i’m little confused about raid 10 , but your step by step guide is very helpful.

    • Adam Strohl

      Thank you, but I would not recommend striped + mirrored ZFS as it has less redundancy than a RAIDZ2 would. Any two disks could fail and the RAID would continue working with RAIDZ2. With striped and mirrored vdevs (“RAID10” with ZFS) if you lose two disk within the same stripe your array will fail.

  5. Sigmar Wiesmayr


    thanks for this great instructions.

    A detail, perhaps I am wrong, but at step 6, shouldn’t it be
    echo ‘geom_mirror_load=”YES”‘ >> /mnt/boot/loader.conf and
    echo ‘daily_status_gmirror_enable=”YES”‘ >> /mnt/etc/periodic.conf


    • Adam Strohl

      Hey Sigmar, the instructions in step 6 are correct as the “final changes” shell chroots to the new filesystem. So all paths should not have /mnt in front of them at that step.

  6. Rags

    What’s the advantages/disadvantages of mirroring the partitions like you do, over just mirroring the whole disk similar to what is shown in chapter 18.3 of the FreeBSD documentation, and then partitioning the mirrored devices afterwards?

    I’m specifically thinking for a server, that has two dedicated SSD’s for the OS, and a bunch of spindles for storage.

    • Adam Strohl

      Hello, the start of the article states why mirroring the entire disk can be problematic when using GPT (at least when this article was originally written, in the 9.x era).

  7. Fabiola

    It didn’t work for me…I get error 19 at boot 🙁
    Mounting from ufs:/dev/mirror/root failed with error 19.

  8. Tim

    See the NOTES section of the gmirror man page where it suggests ‘-b prefer’ is needed for mirrored swap to assure savecore(8) can find a kernel dump. Thanks for the posting.

    • Adam Strohl

      Excellent feedback Tim, I’ve updated the article to reflect this, thank you!

  9. Izydor

    Just used these instructions with 12.1 and everything went smoothly. Thank you very much for sharing this. This is my first time setting up mirroring and so I’m wondering about ensuring proper kernel dumps. You say that using -b prefer
    “will reduce performance to the equivalent of a single physical disk as I/O operations will no longer use both simultaneously.”
    Do you mean this will reduce performance strictly for I/O from/to swap or for all partitions? I’ve read quite a bit about geom and gmirror but I’m very confused on this point. Please forgive my ignorance.

    • Adam Strohl

      Glad it helped! The “-b prefer” flat would reduce I/O on the GMIRROR volumes, in this case just swap.


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